1. Field of the Invention
The present invention relates to a film deposition apparatus and a film deposition method for depositing a film on a substrate by carrying out plural cycles of supplying in turn at least two source gases to the substrate in order to form a layer of a reaction product, and a computer readable storage medium storing a computer program for causing the film deposition apparatus to carry out the film deposition method.
2. Description of the Related Art
As a film deposition technique in a semiconductor fabrication process, there has been known a so-called Atomic Layer Deposition (ALD) or Molecular Layer Deposition (MLD). In such a film deposition technique, a first reaction gas is adsorbed on a surface of a semiconductor wafer (referred to as a wafer hereinafter) under vacuum and then a second reaction gas is adsorbed on the surface of the wafer in order to foam one or more atomic or molecular layers through reaction of the first and the second reaction gases on the surface of the wafer; and such an alternating adsorption of the gases is repeated plural times, thereby depositing a film on the wafer. This technique is advantageous in that the film thickness can be controlled at higher accuracy by the number of times alternately supplying the gases, and in that the deposited film can have excellent uniformity over the wafer. Therefore, this deposition method is thought to be promising as a film deposition technique that can address further miniaturization of semiconductor devices.
Such a film deposition method may be preferably used, for example, for depositing a dielectric material to be used as a gate insulator. When silicon dioxide (SiO2) is deposited as the gate insulator, a bis (tertiary-butylamino) silane (BTBAS) gas or the like is used as a first reaction gas (source gas) and ozone gas or the like is used as a second gas (oxidation gas).
In order to carry out such a deposition method, use of a single-wafer deposition apparatus having a vacuum chamber and a shower head at a top center portion of the vacuum chamber has been under consideration. In such a deposition apparatus, the reaction gases are introduced into the chamber from the top center portion, and unreacted gases and by-products are evacuated from a bottom portion of the chamber. When such a deposition chamber is used, it takes a long time for a purge gas to purge the reaction gases, resulting in an extremely long process time because the number of cycles may reach several hundred. Therefore, a deposition method and apparatus that enable high throughput is desired.
Under these circumstances, film deposition apparatuses having a vacuum chamber and a rotation table that holds plural wafers along a rotation direction have been proposed.
Patent Document 1 listed below discloses a deposition apparatus whose process chamber is shaped into a flattened cylinder. The process chamber is divided into two half circle areas. Each area has an evacuation port provided to surround the area at the top portion of the corresponding area. In addition, the process chamber has a gas inlet port that introduces separation gas between the two areas along a diameter of the process chamber. With these configurations, while different reaction gases are supplied into the corresponding areas and evacuated from above by the corresponding evacuation ports, a rotation table is rotated so that the wafers placed on the rotation table can alternately pass through the two areas. A separation area to which the separation gas is supplied has a lower ceiling than the areas to which the reaction gases are supplied.
However, because the reaction gases and the separation gas are supplied downward and then evacuated upward from the evacuation ports provided at the upper portion of the chamber, particles in the chamber may be blown up by the upward flow of the gases and fall on the wafers, leading to contamination of the wafers.
Patent Document 2 discloses a process chamber having a wafer support member (rotation table) that holds plural wafers and that is horizontally rotatable, first and second gas ejection nozzles that are located at equal angular intervals along the rotation direction of the wafer support member and oppose the wafer support member, and purge nozzles that are located between the first and the second gas ejection nozzles. The gas ejection nozzles extend in a radial direction of the wafer support member. A top surface of the wafers is higher than a top surface of the wafer supporting member, and the distance between the ejection nozzles and the wafers on the wafer support member is about 0.1 mm or more. A vacuum evacuation apparatus is connected to a portion between the outer edge of the wafer support member and the inner wall of the process chamber. According to a process chamber so configured, the purge gas nozzles discharge purge gases to create a gas curtain, thereby preventing the first reaction gas and the second reaction gas from being mixed.
However, the gas curtain cannot completely prevent mixture of the reaction gases but may allow one of the reaction gases to flow through the gas curtain to be mixed with the other reaction gas partly because the gases flow along the rotation direction due to the rotation of the wafer support member. In addition, the first (second) reaction gas discharged from the first (second) gas outlet nozzle may flow through the center portion of the wafer support member to meet the second (first) gas, because centrifugal force is not strongly applied to the gases in a vicinity of the center of the rotating wafer support member. Once the reaction gases are mixed in the chamber, an MLD (or ALD) mode film deposition cannot be carried out as expected.
Patent Document 3 discloses a process chamber that is divided into plural process areas along the circumferential direction by plural partitions. Below the partitions, a circular rotatable susceptor on which plural wafers are placed is provided leaving a slight gap in relation to the partitions. In addition, at least one of the process areas serves as an evacuation chamber. In such a process chamber, process gas introduced into one of the process areas may diffuse into the adjacent process area through the gap below the partition, and be mixed with another process gas introduced into the adjacent process area. Moreover, the process gases may be mixed in the evacuation chamber, so that the wafer is exposed to the two process gases at the same time. Therefore, ALD (or MLD) mode deposition cannot be carried out in a proper manner by this process chamber.
Patent Document 4 discloses a process chamber having four sector-shaped gas supplying plates each of which has a vortex angle of 45 degrees, the four gas supplying plates being located at angular intervals of 90 degrees, evacuation ports that evacuate the process chamber and are located between the adjacent two gas supplying plates, and a susceptor that holds plural wafers and is provided in order to oppose the gas supplying plate. The four gas supplying plates can discharge AsH3 gas, H2 gas, trimethyl gallium (TMG) gas, and H2 gas, respectively. However, Patent Document 4 does not provide any realistic measures to prevent two source gases (AsH3, TMG) from being mixed. Because of the lack of such measures, the two source gases may be mixed around the center of the susceptor and through the H2 gas supplying plates. Moreover, because the evacuation ports are located between the adjacent two gas supplying plates to evacuate the gases upward, particles are blown up from the susceptor surface, which leads to wafer contamination.
Patent Document 5 discloses a process chamber having a circular plate that is divided into four quarters by partition walls and has four susceptors respectively provided in the four quarters, four injector pipes connected into a cross shape, and two evacuation ports located near the corresponding susceptors. In this process chamber, four wafers are mounted in the corresponding four susceptors, and the four injector pipes rotate around the center of the cross shape above the circular plate while ejecting a source gas, a purge gas, a reaction gas, and another purge gas, respectively. In such a process chamber, after one of the injector pipes passes over one of the quarters, this quarter cannot be purged by the purge gas in a short period of time. In addition, the reaction gas in one of the quarters can easily flow into an adjacent quarter. Therefore, it is difficult to perform an MLD (or ALD) mode film deposition.
Furthermore, Patent Document 6 (Patent Documents 7, 8) discloses a film deposition apparatus preferably used for an Atomic Layer CVD method that causes plural gases to be alternately adsorbed on a target (a wafer). In the apparatus, a susceptor that holds the wafer is rotated, while source gases and purge gases are supplied to the susceptor from above. Paragraphs 0023, 0024, and 0025 of the document describe partition walls that extend in a radial direction from a center of a chamber, and gas ejection holes that are formed in a bottom of the partition walls in order to supply the source gases or the purge gas to the susceptor, so that an inert gas as the purge gas ejected from the gas ejection holes produces a gas curtain. Regarding evacuation of the gases, a paragraph 0058 of the document describes that the source gases are evacuated through an evacuation channel 30a, and the purge gases are evacuated through an evacuation channel 30b. With such a configuration, the source gases can flow into a purge gas compartment from source gas compartments located in both sides of the purge gas compartment and be mixed with each other in the purge gas compartment. As a result, a reaction product is generated in the purge gas compartment, which may cause particles to fall onto the wafer.    Patent Document 1: U.S. Pat. No. 7,153,542 (FIGS. 6A, 6B)    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2001-254181 (FIGS. 1, 2)    Patent Document 3: Japanese Patent Publication No. 3,144,664 (FIGS. 1, 2, claim 1)    Patent Document 4: Japanese Patent Application Laid-Open Publication No. H4-287912    Patent Document 5: U.S. Pat. No. 6,634,314    Patent Document 6: Japanese Patent Application Laid-Open Publication No. 2007-247066 (paragraphs 0023 through 0025, 0058, FIGS. 12 and 13)    Patent Document 7: United States Patent Publication No. 2007-218701    Patent Document 8: United States Patent Publication No. 2007-218702